Microsoft Interview Guide: Process, Questions & Tips

Approach 1 — Hash Set (With Extra Space): • Iterate through the string • Check if the character is in the set — if yes, return false; if no, add it • Time: O(n), Space: O(n) Approach 2 — Bit Vector (Without Extra Space): • For ASCII strings (128 chars), use a bit vector • An integer has 32 bits; use a long or two integers to cover all ASCII characters • For each character, compute its bit position • Check if that bit is set (using bitwise AND), and set it (using bitwise OR) • Time: O(n), Space: O(1) Approach 3 — Sorting (No Extra Space, Higher Time): • Sort the string first and check adjacent characters • Time: O(n log n), Space: O(1) if in-place sort Microsoft Tip: Interviewers appreciate when you discuss multiple approaches with tradeoffs before coding the optimal one. Show your decision-making process.

This is a core growth mindset question. A strong answer demonstrates four stages: 1. Received Without Defensiveness: • 'In a code review, a senior engineer pointed out that my API design was tightly coupled and would be difficult to extend.' • 'My initial reaction was defensive — I'd spent a week on it.' 2. Genuine Reflection: • 'But I stepped back and studied the SOLID principles they referenced' • 'I realized they were right — my design violated the Open/Closed principle' 3. Specific Action: • 'I redesigned the interface with dependency injection' • 'This made it testable and extensible' 4. Lasting Change: • 'That feedback fundamentally changed how I approach API design' • 'Now I actively seek design reviews early in my process, before I'm invested in a specific approach' Key Signal: Humility, concrete action, and a permanent behavioral change — not just a one-time fix.